FIG. 1 is a diagram for explaining a concept of direct communication between terminals to which the present invention is applicable.
A general communication scheme is served by an eNB for a plurality of user equipments (UEs). On the contrary, according to a D2D communication scheme, as shown in FIG. 1, if a resource for D2D communication is allocated, direct communication can be performed between a UE 1 and a UE 2.
When a UE performs communication with a different UE using a direct radio channel, it may be able to use a discovery signal as a method of discovering a counterpart UE of the communication. In this case, although the UE corresponds to a terminal of a user, if such a network device as an eNB transmits and receives a signal according to a communication scheme between UEs, the network device can also regarded as a sort of UEs.
In the following, a directly connected link between UEs is referred to as a D2D link and a link used for a UE to perform communication with an eNB is referred to as an eNB-UE link.